I'm sorry, I'm unable to find the "Make Dark" button in the Item Manager, is this available to the contributor? I also have some test clips I uploaded that I would love to remove completely from the index and archive.
The make dark button is only available to people who have their own collection (like a netlabel). If your items are in the open source collections, then you'll need an admin to take them down for you. Here's the info you'll need: